CN114689165B - Sensing device with pre-pressing element - Google Patents

Abstract

The invention discloses a sensing device with a pre-pressing element, which comprises a shell, two piezoelectric elements and the pre-pressing element. The shell comprises a sensing part, a connecting part and a contact part. The sensing part is provided with a space for accommodating the two piezoelectric elements. The contact part is provided with a groove and is connected with the sensing part and the connecting part. The pre-pressing element comprises a pre-pressing part and a cantilever part. The pre-pressing part is suspended above the sensing part. The cantilever part is suspended above the contact part and comprises a fixed end and a free end. The fixed end is connected with the shell the free end is connected with the pre-pressing part.

Description

Sensing device with preload element

Technical Field

The present invention relates to a sensing device, and in particular to a sensing device with a pre-pressure element.

Background Art

Due to the development of smart manufacturing and other industries in the future, the demand for machine tools will grow significantly. The status of the spindle of a machine tool will affect the machining accuracy of the machine tool, so how to effectively monitor the health status of the spindle is a key technology in smart manufacturing.

Currently, there is no sensor device that can directly measure the forces (such as cutting forces) borne by the machine tool spindle. Currently, only indirect methods can be used to infer the cutting forces of the machine tool spindle. For example, the cutting forces of the machine tool spindle are indirectly inferred using the vibration signals measured by the vibration sensor. However, these methods require complex algorithms and cannot accurately measure the various forces borne by the machine tool spindle.

In addition, the existing sensing devices cannot properly fix the piezoelectric elements inside the sensing devices, which seriously affects the performance of the sensing devices and makes it impossible for the sensing devices to obtain accurate sensing results.

In addition, the existing sensing devices cannot properly fix the piezoelectric elements inside the sensing devices, or need to use a jig to press the outer shell of the sensing device to fix the piezoelectric elements inside the sensing device before the subsequent outer shell welding manufacturing process can be carried out. When the jig presses the outer shell of the sensing device, the piezoelectric elements disposed inside the sensing device often break, thereby greatly reducing the manufacturing process yield of these sensing devices.

Summary of the invention

According to one embodiment of the present invention, a sensing device with a prestressing element is proposed, which includes a shell, two piezoelectric elements, a prestressing element and a conductive element. The shell includes a sensing part, a connecting part and a contact part. The sensing part includes a bottom plate and an outer wall. The outer wall is arranged on the bottom plate so that a space is formed between the outer wall and the bottom plate. The connecting part has a hole that passes through the connecting part. The contact part has a groove and connects the sensing part and the connecting part. Two piezoelectric elements are arranged in this space, and each piezoelectric element has a first electrode and a second electrode. The prestressing element includes a prestressing part and a cantilever part. The prestressing part is arranged above the sensing part. The cantilever part is arranged above the contact part and includes a fixed end and a free end. The fixed end is connected to the contact part and the free end is connected to the prestressing part so as to cause the prestressing part to be displaced in a direction away from the two piezoelectric elements or to be displaced in another direction close to the two piezoelectric elements. The conductive element is arranged between the two piezoelectric elements, wherein the conductive element is electrically connected to the first electrodes of each piezoelectric element, the bottom plate is electrically connected to the second electrode of one of the piezoelectric elements, and the pre-pressing portion is electrically connected to the second electrode of the other piezoelectric element.

According to another embodiment of the present invention, a sensing device with a prestressing element is provided, which includes a housing, two piezoelectric elements and a prestressing element. The housing includes a sensing part, a connecting part and a contact part. The sensing part includes a bottom plate, an inner wall and an outer wall. The bottom plate has a through hole. The inner wall is arranged on the bottom plate and surrounds the through hole to form a through hole. The outer wall is arranged on the bottom plate so that a space is formed between the outer wall and the bottom plate. The connecting part has a hole penetrating the connecting part. The contact part has a groove and connects the sensing part and the connecting part. Two piezoelectric elements are arranged in this space, and each piezoelectric element has a first electrode and a second electrode. The prestressing element includes a prestressing part and a cantilever part. The prestressing part is arranged above the sensing part. The cantilever part is arranged above the contact part and includes a fixed end and a free end. The fixed end is connected to the contact part and the free end is connected to the prestressing part so that the prestressing part is displaced in a direction away from the two piezoelectric elements or in another direction close to the two piezoelectric elements.

The above description of the content of the present invention and the following description of the implementation modes are used to demonstrate and explain the spirit and principle of the present invention, and to provide a further explanation of the scope of the patent application of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG1 is a structural diagram of a sensing device with a pre-load element according to a first embodiment of the present invention;

FIG2 is a structural diagram of a housing of a sensing device with a pre-compression element according to a first embodiment of the present invention;

3 is a structural diagram of a pre-pressing element of a sensing device with a pre-pressing element according to a first embodiment of the present invention;

4 is a schematic diagram of a pre-pressing element of a sensing device with a pre-pressing element according to a first embodiment of the present invention;

5 is a cross-sectional view of a sensing device with a pre-load element according to a first embodiment of the present invention;

6 is a schematic diagram of a sensing device with a pre-load element installed on a spindle collar according to a first embodiment of the present invention;

7 is a structural diagram of a sensing device with a pre-compression element according to a second embodiment of the present invention;

8 is a structural diagram of a housing of a sensing device with a pre-compression element according to a second embodiment of the present invention;

FIG. 9 is a structural diagram of a pre-pressing element of a sensing device with a pre-pressing element according to a second embodiment of the present invention.

Explanation of symbols

1,2: Sensing device

11,21: Shell

111,211:Sensor

1111,2111: bottom plate

1112:Inner wall

1113,2113:Exterior wall

112,212: Connecting part

113,213: Contact part

12,22: Piezoelectric element

121,221: first electrode

122,222: Second electrode

13,23: Preload element

131,231: Pre-pressing part

132,232: Cantilever

14,24: Conductive elements

15,25: Cable

151:Signal line

152: Ground

16,26: Electrical insulation sleeve

17: Protective case

F1: Fixed end

F2: Free end

T:Piercing

H: Hole

S,S’: Space

L: Groove

S _d : spindle

R: Ring

P: Contact

K: Connecting element

DETAILED DESCRIPTION

The following will refer to the relevant drawings to illustrate an embodiment of a sensing device with a preload element according to the present invention. For the sake of clarity and convenience of the illustration, the components in the drawings may be exaggerated or reduced in size and proportion. In the following description and/or claims, when it is mentioned that an element is "connected" or "coupled" to another element, it may be directly connected or coupled to the other element or there may be an intervening element; and when it is mentioned that an element is "directly connected" or "directly coupled" to another element, there is no intervening element, and other words used to describe the relationship between elements or layers should be interpreted in the same way. For ease of understanding, the same elements in the following embodiments are illustrated with the same symbols.

Please refer to Figures 1, 2 and 3, which are structural diagrams of a sensing device with a pre-stressing element, a structural diagram of a housing of the sensing device with a pre-stressing element and a structural diagram of a pre-stressing element of the sensing device with a pre-stressing element according to a first embodiment of the present invention. As shown in Figure 1, the sensing device 1 includes a housing 11, two piezoelectric elements 12, a pre-stressing element 13, a conductive element 14, a cable 15 and an electrical insulating sleeve 16.

As shown in FIG2 , the housing 11 includes a sensing portion 111, a connecting portion 112 and a contact portion 113. The sensing portion 111 includes a bottom plate 1111, an inner wall 1112 and an outer wall 1113. The inner wall 1112 and the outer wall 1113 are disposed on the bottom plate 111. The bottom plate 1111 of the sensing portion 111 is conductive, while the connecting portion 112 and the contact portion 113 are conductive. The bottom plate 1111 has a through hole, and the inner wall 1112 surrounds the through hole to form a through hole T. An annular space S is formed between the inner wall 1112 and the outer wall 1113. The connecting portion 112 has a hole H that penetrates the connecting portion 112. The contact portion 113 has a groove L, and the sensing portion 111 is connected to the connecting portion 112 through the contact portion 113. In this embodiment, the sensing portion 111 may be in a circular shape; in another embodiment, the sensing portion 111 may also be in an elliptical, polygonal, trapezoidal, irregular or other shapes.

As shown in FIG. 1 and FIG. 2 , two piezoelectric elements 12 are disposed in an annular space S formed by the inner wall 1112, the outer wall 1113 and the bottom plate 1111 of the sensing portion 111. Each piezoelectric element 12 has a first electrode 121 and a second electrode 122. In addition, each piezoelectric element 12 has a central hole so that the shape of each piezoelectric element 12 can correspond to the shape of the annular space S of the sensing portion 111, so that each piezoelectric element 12 can be disposed in the annular space S.

As shown in FIGS. 1 to 3 , the pre-stressing element 13 includes a pre-stressing portion 131 and a cantilever portion 132, and both the pre-stressing portion 131 and the cantilever portion 132 are conductive. The pre-stressing portion 131 is suspended above the sensing portion 111 to cover the two piezoelectric elements 12. In addition, the pre-stressing portion 131 also has a central hole, so that the shape of the pre-stressing portion 131 corresponds to the shape of the two piezoelectric elements 12 and the shape of the annular space S of the sensing portion 111. The cantilever portion 132 is suspended above the contact portion 113 and includes a fixed end F1 and a free end F2. The fixed end F1 of the cantilever portion 132 is connected to the contact portion 113, and the free end F2 of the cantilever portion 132 is connected to the pre-stressing portion 131, so that the pre-stressing portion 131 has the function of generating a displacement in a direction away from the two piezoelectric elements 12 or generating another displacement in another direction close to the two piezoelectric elements 12. Furthermore, when the pre-stressing portion 131 is subjected to an external force and displaced in a direction away from the two piezoelectric elements 12 , the cantilever portion 132 can generate a restoring force in a direction toward the two piezoelectric elements 12 , so that the pre-stressing portion 131 can generate a pre-stress and apply the pre-stress to the two piezoelectric elements 12 .

In addition, the cantilever portion 132 may also include two fixed end extension portions E. The two fixed end extension portions E are arranged on both sides of the fixed end F1 and are connected to the contact portion 113 of the shell 11. The fixed end F1 of the cantilever portion 132 and the two fixed end extension portions E form a U-shape. Through this structural design, the restoring force generated by the pre-stressing element 13 can be adjusted by changing the length of the two fixed end extension portions E. When the pre-stressing portion 131 is to produce the same displacement, the longer the length of the two fixed end extension portions E, the greater the restoring force generated by the pre-stressing element 13. Conversely, when the pre-stressing portion 131 is to produce the same displacement, the shorter the length of the two fixed end extension portions E, the smaller the restoring force generated by the pre-stressing element 13. The lengths of the two fixed end extension portions E can be adjusted for different applications to meet the needs of different situations.

Please refer to FIG. 4 , which is a schematic diagram of a pre-stressing element of a sensing device with a pre-stressing element according to a first embodiment of the present invention. As shown in the figure, each piezoelectric element 12 has a first electrode 121 and a second electrode 122. In this embodiment, one piezoelectric element 12 is disposed on the bottom plate 1111 of the sensing portion 111 and contacts the bottom plate 1111. A conductive element 14 is disposed on the piezoelectric element 12 and another piezoelectric element 12 is disposed on the conductive element 14, so that the conductive element 14 is disposed between the two piezoelectric elements 12. Therefore, the conductive element 14 can electrically connect the first electrode 121 of each piezoelectric element 12. Through the above structure, the bottom plate 1111 of the sensing portion 111 can be electrically connected to the second electrode 122 of one of the piezoelectric elements 12, and the pre-stressing portion 131 of the pre-stressing element 13 can be electrically connected to the second electrode 122 of another piezoelectric element 12. In one embodiment, the conductive element 14 can be a metal sheet, such as a copper sheet, an iron sheet or other conductive elements.

When the pre-stressing portion 131 of the pre-stressing element 13 is subjected to an external force and displaced in a direction away from the two piezoelectric elements 12, the cantilever portion 132 of the pre-stressing element 13 can generate a restoring force in a direction close to the two piezoelectric elements 12. This restoring force causes the pre-stressing portion 131 of the pre-stressing element 13 to press against one of the piezoelectric elements 12, so that the pre-stressing portion 131 of the pre-stressing element 13 can generate a pre-stress and apply this pre-stress to the two piezoelectric elements 12. Therefore, the pre-stressing element 13 can effectively fix the two piezoelectric elements 12 inside the sensing device 1 through the above-mentioned pre-stress. As can be seen from the above, the pre-stressing element 13 can generate a pre-stress and apply this pre-stress to the two piezoelectric elements 12, so that the phenomenon of poor contact between the piezoelectric element 12 and the electrical channel can be avoided, thereby improving the accuracy and sensitivity of the sensing device 1. In addition, the pre-pressure generated by the pre-pressure element 13 can also effectively fix the two piezoelectric elements 12 to prevent the two piezoelectric elements 12 from being deformed and displaced and damaged, thereby effectively improving the manufacturing yield of the sensing device 1 and the reliability of future use.

As shown in FIG. 1 and FIG. 2 , the cable 15 passes through the hole H of the connecting portion 112 and extends to the groove L of the contact portion 113 and is connected to the conductive element 14. In addition, the electrical insulating sleeve 16 covers a portion of the cable 15 and a portion of the conductive element 14 to provide electrical insulation. In one embodiment, the electrical insulating sleeve 16 can be a heat shrink tube, insulating glue, tape or other similar electrical insulating elements.

Please refer to FIG5 , which is a cross-sectional view of a sensing device with a preload element according to the first embodiment of the present invention. As shown in the figure, the cable 15 includes a signal line 151 and a ground line 152. The ground line 152 is a hollow tubular structure. The ground line 152 surrounds the signal line 151 and is electrically insulated from the signal line 151.

The signal line 151 is connected to the conductive element 14 to form a first electrical channel. The electrical insulating sleeve 16 covers the signal line 151 , the conductive element 14 and the contact point P connecting the signal line 151 and the conductive element 14 .

In addition, as mentioned above, the pre-stressing portion 131 and the cantilever portion 132 of the pre-stressing element 13 are both conductive, and the bottom plate 1111, the contact portion 113 and the connecting portion 112 of the sensing portion 111 of the housing 11 are all conductive. As can be seen from FIG. 5 , the ground wire 152 of the cable 15 is connected to the connecting portion 112 of the housing 11. The fixed end F1 of the cantilever portion 132 of the pre-stressing element 13 is connected to the contact portion 113 of the housing. Therefore, the connecting portion 112 of the housing 11 is connected to the pre-stressing portion 131 of the pre-stressing element 13 through the cantilever portion 132 of the pre-stressing element 13. The pre-stressing portion 131 of the pre-stressing element 13 contacts the second electrode 122 of one of the piezoelectric elements 12. Therefore, the ground wire 152 of the cable 15, the connecting portion 112 of the shell 11, the cantilever portion 132 of the pre-stressing element 13 and the pre-stressing portion 131 can form a second electrical channel so that the ground wire 152 of the cable 15 can be electrically connected to the second electrode 122 contacted by the pre-stressing portion 131.

In addition, the ground wire 152 of the cable 15 is connected to the connection portion 112 of the housing 11, and the connection portion 112 of the housing 11 is connected to the bottom plate 1111 of the sensing portion 111 of the housing 11 through the contact portion 113 of the housing 11. The bottom plate 1111 of the sensing portion 111 contacts the second electrode 122 of another piezoelectric element 12. Therefore, the ground wire 152 of the cable 15, the connection portion 112 of the housing 11, the contact portion 113, and the bottom plate 1111 of the sensing portion 111 can form another second electrical channel, so that the ground wire 152 of the cable 15 can be electrically connected to the second electrode contacted by the bottom plate 1111.

As shown in Fig. 5, the sensing device 1 may further include a protective sleeve 17, which may cover the contact portion 113 and the connecting portion 112 of the housing 11 and the cable 15 to provide good protection. In one embodiment, the protective sleeve 17 may be a heat shrink tube or other similar components.

As can be seen from the above, the sensing device 1 has a special structural design to provide a complete electrical channel, so the cable 15 can be directly electrically connected to the two piezoelectric elements 12 disposed inside the sensing device 1 without the need for additional connectors or joints. This not only simplifies the assembly process of the sensing device 1, but also reduces the overall volume of the sensing device 1.

Please refer to FIG6 , which is a schematic diagram of the first embodiment of the present invention, wherein the sensing device with a preload element is installed on the spindle collar. As shown in the figure, the sensing portion 111 of the housing 11 of the sensing device 1 has a through hole, so that the sensing device 1 can be stably fixed to the collar R of the spindle S _d of the machine tool through a connecting element K (such as a screw), so that the sensing device 1 can be more effectively integrated with the spindle S _d . Therefore, the sensing device 1 directly measures the force borne by the spindle S _d of the machine tool, so no complex algorithm is required, thereby effectively reducing the cost.

Of course, the above is only an example, and the structure of each component of the sensing device 1, the connection relationship of each component and the operation mode can be changed according to actual needs, and the present invention is not limited thereto.

It is worth mentioning that there is currently no sensing device that can directly measure the force (such as cutting force) borne by the machine tool spindle. Currently, only indirect methods can be used to infer the cutting force of the machine tool spindle. For example, the cutting force of the machine tool spindle is indirectly inferred using the vibration signal measured by the vibration sensor. However, these methods require complex algorithms and cannot accurately measure the various forces borne by the machine tool spindle. On the contrary, according to an embodiment of the present invention, the sensing device can be arranged on a spindle collar mounted on the machine tool, so that it can be effectively integrated with the spindle to directly measure the various forces borne by the spindle, so that no complex algorithms are required and the accuracy of the measurement can be effectively improved.

Furthermore, according to an embodiment of the present invention, the sensing portion of the housing of the sensing device has a through hole, through which a connecting element (such as a screw) can be screwed, so that the sensing device can be stably fixed to the spindle collar of the machine tool, so that the sensing device can be more effectively integrated with the spindle.

In addition, the existing sensing devices cannot properly fix the piezoelectric elements inside the sensing devices, which seriously affects the performance of these sensing devices and makes them unable to obtain accurate sensing results. On the contrary, according to an embodiment of the present invention, the sensing device has a pre-pressure element, which can apply appropriate pre-pressure to the piezoelectric element inside the sensing device, so that the effective force-bearing area of the piezoelectric element is increased, thereby effectively improving the measurement sensitivity of the sensing device.

In addition, the existing sensing devices cannot properly fix the piezoelectric elements inside the sensing devices, or need to use a jig to press the outer shell of the sensing device, and then fix the piezoelectric elements inside the sensing device before the subsequent outer shell welding manufacturing process can be carried out. When the jig presses the outer shell of the sensing device, the piezoelectric elements disposed inside the sensing device often break, thereby greatly reducing the manufacturing process yield of these sensing devices. On the contrary, according to an embodiment of the present invention, the sensing device has a cantilever beam pre-stressing element, which can apply appropriate pre-stress to the piezoelectric element inside the sensing device, that is, the piezoelectric element can be effectively fixed inside the sensing device to avoid the piezoelectric element from breaking, thereby greatly improving the manufacturing process yield of the sensing device assembly.

Furthermore, according to an embodiment of the present invention, the sensing device has a special structural design, so that the piezoelectric element disposed in the sensing device can be directly electrically connected to the cable without the need for an additional connector or joint, thereby simplifying the steps of assembling the sensing device to the spindle. The following describes in more detail the electrical connection method between the piezoelectric element and the cable.

Please refer to Figures 7, 8 and 9, which are structural diagrams of a sensing device with a pre-stressing element, a structural diagram of a housing of the sensing device with a pre-stressing element and a structural diagram of a pre-stressing element of the sensing device with a pre-stressing element according to a second embodiment of the present invention. As shown in Figure 7, the sensing device 2 includes a housing 21, two piezoelectric elements 22, a pre-stressing element 23, a conductive element 24, a cable 25 and an electrical insulating sleeve 26.

As shown in FIG8 , the housing 21 includes a sensing portion 211, a connecting portion 212 and a contact portion 213. Different from the aforementioned embodiment, the sensing portion 211 includes a bottom plate 2111 and an outer wall 2113 but does not include an inner wall, and the bottom plate 2111 does not have a through hole. Similarly, the outer wall 2113 is disposed on the bottom plate 211 and surrounds the bottom plate 211 to form a space S’. The bottom plate 2111 of the sensing portion 211 is conductive, while the connecting portion 212 and the contact portion 213 are conductive. The connecting portion 212 has a hole H that passes through the connecting portion 212. The contact portion 213 has a groove L, and the sensing portion 211 is connected to the connecting portion 212 through the contact portion 213. In this embodiment, the sensing portion 211 may be disc-shaped. In another embodiment, the sensing portion 211 may also be elliptical, polygonal, trapezoidal, irregular or other shapes.

As shown in Fig. 7 and Fig. 8, two piezoelectric elements 22 are disposed in a space S' formed by the outer wall 2113 and the bottom plate 2111 of the sensing portion 211. Each piezoelectric element 22 has a first electrode 221 and a second electrode 222. Different from the first embodiment, each piezoelectric element 22 does not have a central hole.

As shown in FIGS. 7 to 9 , the pre-stressing element 23 includes a pre-stressing portion 231 and a cantilever portion 232, and both the pre-stressing portion 231 and the cantilever portion 232 are conductive. The pre-stressing portion 231 is suspended above the sensing portion 211 to cover the two piezoelectric elements 22. Unlike the first embodiment, the pre-stressing portion 231 does not have a central hole. The cantilever portion 232 is suspended above the contact portion 213 and includes a fixed end F1 and a free end F2. The fixed end F1 of the cantilever portion 232 is connected to the contact portion 213, and the free end F2 of the cantilever portion 232 is connected to the pre-stressing portion 231.

The cable 25 passes through the hole H of the connecting portion 212 and extends to the groove L of the contact portion 213, and is connected to the conductive element 24. The electrical insulating sleeve 26 covers a portion of the cable 25 and a portion of the conductive element 24 to provide electrical insulation.

Except for the structure of the sensing portion 211 of the shell 21, the structure of the pre-pressing portion 231 of the pre-pressing element 23 and the structure of the two piezoelectric elements 22, the structures of other elements of the sensing device 2, the connection relationship and operation mode of each element are similar to those of the first embodiment, so they are not described in detail here.

As can be seen from the above, the sensing portion 211 of the housing 21 includes a bottom plate 2111 and an outer wall 2113 but does not include an inner wall, so that the sensing portion 211 of the housing 21 is disc-shaped. Therefore, the sensing device 2 is not limited to the application of measuring the cutting force of the spindle of the machine tool, and can also be installed in other positions to achieve various applications, so that the application range of the sensing device 2 is wider.

Of course, the above is only an example, and the structure of each component of the sensing device 2, the connection relationship and the operation mode of each component can be changed according to actual needs, and the present invention is not limited thereto.

In summary, according to the embodiments of the present invention, the sensing device can be disposed on a spindle collar mounted on a machine tool, so that it can be effectively integrated with the spindle to directly measure various forces borne by the spindle, so that complex algorithms are not required and the cost can effectively improve the measurement accuracy.

Furthermore, according to an embodiment of the present invention, the sensing portion of the housing of the sensing device has a through hole, through which a connecting element (such as a screw) can be screwed, so that the sensing device can be stably fixed to the spindle collar of the machine tool, so that the sensing device can be more effectively integrated with the spindle.

In addition, according to an embodiment of the present invention, the sensing device has a cantilever beam pre-stressing element, which can apply appropriate pre-stress to the piezoelectric element inside the sensing device to increase the effective force-bearing area of the piezoelectric element, thereby effectively improving the measurement sensitivity of the sensing device.

In addition, according to an embodiment of the present invention, the sensing device has a cantilever beam pre-stressing element, which can apply appropriate pre-stressing force to the piezoelectric element inside the sensing device, that is, the piezoelectric element can be effectively fixed inside the sensing device to avoid the piezoelectric element from breaking, thereby greatly improving the yield of the manufacturing process of assembling the sensing device.

Furthermore, according to an embodiment of the present invention, the sensing device has a special structural design, so that the piezoelectric element disposed in the sensing device can be electrically connected to the cable without the need for an additional connector or joint. This not only simplifies the steps of assembling the sensing device to the spindle, but also reduces the overall volume of the sensing device.

It can be seen that the present invention has indeed achieved the desired improved effect by breaking through the existing technology, and it is not easy for people familiar with the technology to think of. Its progressiveness and practicality obviously meet the application requirements of a patent.

The above description is for illustrative purposes only and is not intended to be limiting. Any other equivalent modifications or changes made thereto without departing from the spirit and scope of the present invention should be included in the appended claims.

Claims (29)

1. A sensing device with a pre-load element, comprising: Housing, including: The sensing part comprises: Base plate; and An outer wall is disposed on the base plate and surrounds the base plate to form a space; a connecting portion having a hole extending therethrough; and A contact portion having a groove and connecting the sensing portion and the connecting portion; Two piezoelectric elements are disposed in the space, wherein each of the piezoelectric elements has a first electrode and a second electrode; Preloading components, including: A pre-pressing portion suspended above the sensing portion; and A cantilever portion suspended above the contact portion, wherein the cantilever portion comprises a fixed end and a free end, the fixed end is connected to the housing and the free end is connected to the pre-pressing portion; A conductive element is arranged between the piezoelectric elements, wherein the conductive element is electrically connected to the first electrodes of each of the piezoelectric elements, the base plate is electrically connected to the second electrode of one of the piezoelectric elements, and the pre-stressing portion is electrically connected to the second electrode of another piezoelectric element, and the pre-stressing portion normally provides a pre-stress applied to the piezoelectric elements. 2. The sensing device with a pre-stressing element as claimed in claim 1, wherein when the pre-stressing portion is subjected to an external force and displaced in a direction away from the piezoelectric elements, the cantilever portion generates a restoring force in a direction approaching the piezoelectric elements. 3 . The sensing device with a pre-stressed element as claimed in claim 2 , wherein when the external force is removed, the restoring force causes the pre-stressed portion to press against one of the piezoelectric elements. 4 . The sensing device with a pre-load element as claimed in claim 1 , wherein the fixed end is connected to the contact portion of the housing. 5. The sensing device with a pre-stressing element as described in claim 1, wherein the cantilever portion further comprises two fixed end extension portions, the fixed end extension portions are arranged on both sides of the fixed end and connected to the contact portion of the shell. 6 . The sensing device with a pre-pressing element as claimed in claim 1 , wherein the sensing portion further comprises an inner wall, and the inner wall is disposed on the bottom plate. 7 . The sensing device with a pre-pressing element as claimed in claim 6 , wherein the bottom plate has a through hole, and the inner wall surrounds the through hole to form a through hole. 8 . The sensing device with a pre-stressing element as claimed in claim 1 , further comprising an electric cable, wherein the electric cable comprises a signal line and a ground line, wherein the ground line surrounds the signal line and is electrically insulated from the signal line. 9 . The sensing device with a pre-stressing element as claimed in claim 8 , wherein the signal line is connected to the conductive element so that the signal line is electrically connected to the first electrode of each of the piezoelectric elements. 10. A sensing device with a pre-stressing element as described in claim 8, wherein the pre-stressing portion and the cantilever portion of the pre-stressing element are both conductive, the contact portion and the connecting portion of the shell are both conductive, the ground wire is connected to the connecting portion, the pre-stressing portion contacts the second electrode of one of the piezoelectric elements, and the ground wire is electrically connected to the second electrode of the piezoelectric element via the connecting portion, the contact portion, the cantilever portion and the pre-stressing portion. 11. A sensing device with a pre-stressed element as described in claim 10, wherein the base plate of the sensing portion of the shell is conductive, the ground wire is connected to the connecting portion and the base plate contacts the second electrode of another piezoelectric element, and the ground wire is electrically connected to the second electrode of the piezoelectric element via the connecting portion, the contact portion and the base plate. 12 . The sensing device with a pre-pressure element as claimed in claim 8 , further comprising an electrical insulation sleeve, wherein the electrical insulation sleeve covers the signal line, the conductive element and a contact, wherein the contact connects the signal line and the conductive element. 13 . The sensing device with a pre-pressure element as claimed in claim 8 , further comprising a protective cover, wherein the protective cover covers the contact portion, the connecting portion and the cable. 14 . The sensing device with a pre-pressed element as claimed in claim 13 , wherein the protective sleeve is a heat shrink tube. 15 . The sensing device with a pre-load element as claimed in claim 1 , wherein the sensing portion is circular, elliptical, polygonal, trapezoidal or irregular in shape. 16. A sensing device with a pre-load element, comprising: Housing, including: The sensing part comprises: a bottom plate having a through hole; an inner wall disposed on the bottom plate and surrounding the through hole to form a through hole; and An outer wall is disposed on the bottom plate and surrounds the bottom plate, so that an annular space is formed between the outer wall and the inner wall; a connecting portion having a hole extending therethrough; and A contact portion having a groove and connecting the sensing portion and the connecting portion; Two piezoelectric elements are disposed in the space, wherein each of the piezoelectric elements has a first electrode and a second electrode; and Preloading components, including: A pre-pressing portion suspended above the sensing portion; and The cantilever part is suspended above the contact part, wherein the cantilever part comprises a fixed end and a free end, the fixed end is connected to the shell and the free end is connected to the pre-pressing part, and the pre-pressing part normally provides a pre-pressure to be applied on the piezoelectric elements. 17 . The sensing device with a pre-stressing element as claimed in claim 16 , wherein when the pre-stressing portion is subjected to an external force and displaced in a direction away from the piezoelectric elements, the cantilever portion generates a restoring force in a direction approaching the piezoelectric elements. 18 . The sensing device with a pre-stressed element as claimed in claim 17 , wherein when the external force is removed, the restoring force causes the pre-stressed portion to press against one of the piezoelectric elements. 19. The sensing device with a pre-load element as claimed in claim 16, wherein the fixed end is connected to the contact portion of the housing. 20 . The sensing device with a pre-load element as claimed in claim 16 , wherein the cantilever portion further comprises two fixed end extension portions, the fixed end extension portions are disposed on two sides of the fixed end and connected to the contact portion of the housing. 21. The sensing device with a pre-stressing element as described in claim 16 further comprises a conductive element, wherein the conductive element is electrically connected to the first electrode of each of the piezoelectric elements, the base plate is electrically connected to the second electrode of one of the piezoelectric elements, and the pre-stressing portion is electrically connected to the second electrode of another of the piezoelectric elements. 22 . The sensing device with a pre-stressing element as claimed in claim 21 , further comprising an electric cable, the electric cable comprising a signal line and a ground line, wherein the ground line surrounds the signal line and is electrically insulated from the signal line. 23 . The sensing device with a pre-stressing element as claimed in claim 22 , wherein the signal line is connected to the conductive element so that the signal line is electrically connected to the first electrode of each of the piezoelectric elements. 24. A sensing device with a pre-stressing element as described in claim 22, wherein the pre-stressing portion and the cantilever portion of the pre-stressing element are both conductive, the contact portion and the connecting portion of the shell are both conductive, the ground wire is connected to the connecting portion, the pre-stressing portion contacts the second electrode of one of the piezoelectric elements, and the ground wire is electrically connected to the second electrode of the piezoelectric element via the connecting portion, the contact portion, the cantilever portion and the pre-stressing portion. 25. A sensing device with a pre-stressed element as described in claim 22, wherein the base plate of the sensing portion of the shell is conductive, the ground wire is connected to the connecting portion, the base plate contacts the second electrode of another piezoelectric element, and the ground wire is electrically connected to the second electrode of the piezoelectric element via the connecting portion, the contact portion and the base plate. 26 . The sensing device with a pre-pressure element as claimed in claim 22 , further comprising an electrical insulation sleeve, wherein the electrical insulation sleeve covers the signal line, the conductive element and a contact, wherein the contact connects the signal line and the conductive element. 27 . The sensing device with a pre-stressing element as claimed in claim 22 , further comprising a protective cover, wherein the protective cover covers the contact portion, the connecting portion and the cable. 28. The sensing device with a pre-stressed element as claimed in claim 27, wherein the protective sleeve is a heat shrink tube. 29. The sensing device with a pre-load element as claimed in claim 16, wherein the sensing portion is circular, elliptical, polygonal, trapezoidal or irregular in shape.